Angewandte Chemie International Edition
10.1002/anie.201704793
COMMUNICATION
suggested that small tumor nodules could be targeted by gGlu-
HMSeR and eradicated by PDT.
We would like to emphasize that the ability to suppress non-
specific phototoxicity in normal tissues is a critical advantage of an
activatable photosensitizer. In order to confirm that gGlu-HMSeR
meets this requirement, we utilized chick chorioallantoic
enable gGlu-HMSeR to be applied topically to the tumor area,
reducing the risk of photodamage to normal tissues, compared to
systemic administration. We believe this is a promising approach
to achieve highly tumor-specific PDT.
membrane (CAM), which is a widely used model for evaluating
drug toxicity and angiogenesis inhibitors[14]. By using the CAM, it
Keywords: activatable photosensitizer • -glutamyl
transpeptidase• intramolecular spirocyclization •seleno-
rhodamine
is possible to quantitatively evaluate the phototoxicity to normal
tissue by scoring the level of vessel occlusion. Moreover, a tumor-
bearing CAM model can be produced by xenografting tumor
spheroids onto CAM, so that we can evaluate therapeutic efficacy
for tumor and phototodamage to normal tissues simultaneously.
First, we used CAM as a normal tissue model by topically
applying gGlu-HMSeR and HMSeR into plastic rings on the CAM,
followed by irradiation at 532 nm with an LED. After 24 hours,
vessel occlusion was evaluated by fluorescence angiography with
FITC-dextran. As shown in Figure 4a, no marked phototoxicity
was seen with gGlu-HMSeR, whereas vessel occlusion was
potently induced in the presence of HMSeR. Next, we examined
the PDT efficacy with a tumor-bearing CAM model in order to see
whether gGlu-HMSeR can induce cell death in millimeter-sized
tumors, since it is difficult to selectively ablate such tiny tumors
with general photosensitizers via the EPR effect. A549-Luc-C8
spheroids were implanted onto CAMs, and after 2 days, the
bioluminescence intensities of the spheroids were evaluated (day 1).
Then, gGlu-HMSeR was topically applied by dropping a solution
onto the tumor and its surrounding area on the CAM, followed by
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incubation for 30 minutes for activation, and then photoirradiation
2
(
532 nm LED, 50 mW/cm , 30 min). This PDT procedure was
repeated 2 days later (day 3; two treatments in total) and the
luminescence was measured on the following day (day 5).
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In conclusion, we have developed the first aminopeptidase-
targeting activatable photosensitizer. This is important, because
various peptidases are overexpressed in different types of tumors.
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a
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we consider that gGlu-HMSeR is converted to HMSeR on the
surface of the cells, and HMSeR is then internalized into the cells
due to its greater hydrophobicity, and accumulates mainly in
lysosomes. This is similar to the mechanism in the case of our
previously reported GGT-targeting activatable fluorescent probe
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spheroids was limited, it should be possible to overcome this issue
by utilizing drug penetration-enhancing techniques such as
ointments . Since gGlu-HMSeR utilizes a simple enzymatic
reaction for activation, sufficient amounts of photosensitizer to
induce cell death could be accumulated at tumor sites within a
short time, of the order of minutes. This rapid activation should
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